The present invention is related to the field of simulator systems that provide haptic or tactile feedback to a user, and more particularly to such simulators used to train physicians in the use of a set of catheters or similar tubular objects.
There is a trend toward increasing use of xe2x80x9cminimally-invasivexe2x80x9d surgical techniques, meaning techniques in which medical tools are inserted into a patient""s body through a relatively small opening in the skin and manipulated from outside the body. In one example of a minimally invasive surgical technique known as xe2x80x9cballoon angioplastyxe2x80x9d, concentric catheters are inserted into a patient""s body and guided into a restricted blood vessel, such as a cardiac artery or a peripheral blood vessel suffering a blockage. One of the catheters, called a xe2x80x9cballoon catheterxe2x80x9d because it has a balloon-like inflatable chamber near the end, is guided into the blood vessel. The balloon-like chamber is inflated to stretch the vessel in the region of the blockage, so that the restricted passage is enlarged.
Because many of the minimally-invasive procedures now being practiced are relatively new, there is an increased need for training doctors or other medical personnel to perform the procedures. Traditionally, surgical training is performed on animals, cadavers or patients. These training methods all have drawbacks that make them either ineffective or undesirable in some cases. Animals are good for training, but expenses and ethical concerns limit their use. Cadavers are also expensive. Also, because the procedure is inherently complex and has associated risks, it is undesirable for inexperienced doctors to perform the procedure on human patients.
An alternative training method involves the use of a simulator. A simulator includes a set of sensors and actuators that interact with the tools being used by the doctor being trained. The simulator also includes a computer that executes a simulation program that includes a model of the physical environment being simulated. For example, a simulator for diagnostic radiology includes a model of a catheter and a blood vessel in which the catheter is inserted and maneuvered. The simulator senses movement or forces exerted on the tools by the doctor to track the position of the simulated catheter in the simulated vessel. When the simulation indicates that the catheter has bumped against a wall of the blood vessel, the simulator activates devices that provide forces to the tools that mimic the forces that would be experienced by the doctor during the real diagnostic radiology procedure.
It is generally desirable that a medical procedure simulator provide a high degree of realism, so that the maximum benefit is obtained from simulation-based training. In particular, it is desirable that a simulator be capable of mimicking the many combinations of forces and torques that can act on a tool during a medical procedure, these forces being commonly referred to as xe2x80x9chaptic feedbackxe2x80x9d. A simulator that provides realistic haptic feedback enables a doctor to better develop the skill required to manipulate a tool in the precise manner required by the procedure.
One known simulator uses an actuator manufactured by Bertec, Inc. of Columbus, Ohio. The Bertec actuator uses a mouse-like mechanism including a ball in contact with a catheter to sense the catheter""s axial rotation and translation. The Bertec actuator also applies compression to the catheter to simulate frictional forces that act on the catheter and that are felt by the physician during a catheterization procedure.
The Bertec actuator suffers drawbacks. The ball used to sense translation and rotation is directly in contact with the catheter, and may slip on the catheter surface as the catheter is manipulated. Any such slippage reduces the accuracy of the position information provided by the actuator. Also, haptic feedback generated by compression alone is not very realistic. The Bertec device acts like a variable resistor, because the force fed back to the user is caused by the sliding and static friction from the compression device. During real catheterization, the catheter encounters moving elastic tissues which actively push back at the catheter when the tissues are stretched. The Bertec device cannot simulate such active forces, because it is a passive device. Also, simple compression cannot realistically simulate the effect of multiple forces or torques operating in different directions.
Other known actuators and actuator systems used for haptic feedback have features similar to the Bertec device, and thus suffer similar drawbacks.
It would be desirable to improve the realism of simulated medical procedures used in medical training in order to improve the quality of the training. In particular it would be desirable to have an actuator system having highly accurate sensors and actuators capable of providing realistic haptic feedback, so that physicians can train effectively before performing medical procedures on patients.
In accordance with the present invention, an actuator is disclosed in which the translational and rotational positions of an elongated object are tracked with high accuracy. The actuator is employed to provide the user with realistic haptic feedback in a simulator such as a surgical simulator.
In one embodiment the actuator includes a plurality of motors and a mechanical interface mechanically coupling the motors to the object. The mechanical interface is configured to apply mutually independent axial force and axial torque to the object in response to respective torques generated by the motors in response to drive signals supplied to the motors. One such mechanical interface employs a carriage assembly including a pair of pinch roller wheels mechanically coupled to one of the motors. The pinch roller wheels are located on opposite sides of the elongated object, and can be clamped over the object such that the wheels engage the object. When the wheels engage the object, the rotation of the wheels via activation of the motors causes the object to be translated axially.
By virtue of its ability to apply independent axial force and torque to the object, the actuator can provide more realistic haptic feedback to the user of the object. Additionally, the pinch roller wheels enable the actuator to securely grip the object throughout its motion, so that the object""s position can be accurately sensed.
In another embodiment the actuator employs first and second bearings each having an interior portion surrounding a central opening through which the object extends. The interior portion of the first bearing is cooperatively configured with the object such that the first bearing and the object can be freely moved with respect to each other in the direction of the longitudinal axis of the object, and the first bearing and the object are coupled for joint rotation about the longitudinal axis of the object. In addition to the interior portion, the second bearing has an outer portion, and is configured such that the outer portion and the object can freely rotate with respect to each other about the longitudinal axis of the object, and the second bearing and the object are mutually coupled for joint movement in the direction of the longitudinal axis of the object. The actuator also includes motors coupled respectively to the bearings for actuation thereof, and sensors that generate sense signals indicative of the translational and rotational positions of the object.
This second actuator embodiment has excellent mechanical coupling between each motor and the object, so that backlash is reduced and accuracy is improved. In part this benefit arises from the cooperative configuration of each bearing and the object. In the disclosed actuator the opening in each bearing is square, as is the cross-section of the object, so that the bearings and the object are tightly coupled for rotation together. The disclosed actuator also employs belt or cable drive between each motor and the corresponding bearing, further improving mechanical coupling between each motor and the object.
Other aspects, features, and advantages of the present invention are disclosed in the detailed description which follows.